The present invention relates to room temperature vulcanizable silicone elastomeric compositions. More particularly, the present invention relates to room temperature vulcanizable silicone compositions which cure upon exposure to atmospheric moisture to self-bonding silicone elastomeric compositions.
Room temperature vulcanizable silicone elastomeric compositions curable through a number of mechanisms are known in the art. Of special interest in the present application are room temperature vulcanizable silicone elastomers which cure upon exposure to moisture through hydrolyzable functionality. These materials are generally prepared by mixing an organopolysiloxane, which is primarily a diorganopolysiloxane, containing silicon-bonded hydroxyl groups with a suitable crosslinking agent either in the presence or absence of added filler, plasticizers, sag control agents and the like. Perhaps the best example of such a composition is disclosed in U.S. Pat. No. 4,395,526 to White et al. which is incorporated by reference into the instant disclosure.
While these room temperature vulcanizable silicone elastomers are extremely useful and commercially successful, the adhesion of these materials to various substrates provides a continuing problem. One approach to provide the necessary adhesion of silicone elastomeric materials to all types of substrates has been the development of priming systems. Such priming systems are undesirable in that they require additional steps and additional time in the process of bonding surfaces together.
The preferred approach is to include self-bonding agents in the room temperature vulcanizable silicone composition so that the cured elastomeric composition will satisfactorily adhere to the substrate without the need for a priming system.
Bessmer et al. in U.S. Pat. No. 3,888,815 discloses a self-bonding room temperature vulcanizable silicone rubber composition comprising a linear organopolysiloxane, a filler, an alkyl silicate or a hydrolyzate product of an alkyl silicate and, as a self-bonding agent, a nitrogen functional silane of the formula ##STR2## where R is selected from the group consisting of monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals, E is a hydrolyzable radical selected from the group consisting of alkoxy, phenoxy, halo, aminodialkylamino and tertiary hydroperoxy, and .theta. is a saturated, unsaturated or aromatic hydrocarbon residue functionalized by a member selected from the group consisting of amino, carbonyl, carboxy, isocyano, azo, diazo, thio, thia, dithia, isothiocyano, oxo, oxa, halo, ester, nitrose, sulfhydryl, hydrocarbonylamido and sulfamido and mixtures thereof, and wherein a is a whole number that varies from 0 to 2. Among the commercially more successful self-bonding agents within the scope of Bessmer et al. are gamma-aminopropyltrimethoxysilane and gamma-aminopropyltriethoxysilane.
Pike et al., U.S. Pat. No. 3,033,815, is concerned with the synthesis of organosilicon compounds containing among other possible functional groups a substituted amino group linked to the silicon atom or atoms thereof through an alkylene linkage of at least three carbon atoms and to such organosilicon compounds as new compositions of matter. Such compounds are said to be useful as sizes for fibrous materials, particularly fibrous glass materials employed in combination with thermosetting resins. Both the monomeric and polymeric compounds are also useful as adhesives or as flocculation agents.
Gilkey et al. in U.S. Pat. No. 3,208,971, discloses bis-silyl urea compounds of the general formula ##STR3## in which R" is an alkyl radical or acyl radical of from 1 to 4 carbon atoms or a radical of the formula --CH.sub.2 CH.sub.2 O).sub.n R'" in which n is 1 or 2 and R'" is an alkyl radical of from 1 to 4 carbon atoms, R' is a monovalent hydrocarbon radical of less than 7 carbon atoms, y has an average value from 0 to 3 inclusive, R is a divalent hydrocarbon radical free of aliphatic unsaturation and having from 1 to 18 carbon atoms which is attached to the nitrogen atom of the urea nucleus through a non-aromatic carbon atom and Z is hydrogen or a lower alkyl radical. Such compositions, which are within the scope of the self-bonding agens of the present invention, are said to be useful as adhesives, coatings and as sizing agents for siliceous materials (i.e. the application of such compositions to a siliceous material improves the bond between the siliceous material and organic resins). In addition, such organosilicon compounds are said to be capable of copolymerization with aminoplast resins to form compositions suitable as coatings and bonding agents.
Pepe et al., U.S. Pat. No. 3,671,562, discloses silicon compounds characterized by the presence of a radical of the formula ##STR4## wherein at least one of the three free valences of the silicon atom are bonded directly to hydrolyzable groups such as alkoxy, aryloxy, amino and the like, and/or oxygen which in turn is bonded to other silicon atoms to form a siloxane. These compounds, and more particularly aqueous solutions of the hydrolyzate of the urea substituted silanes, or the partially or totally condensed siloxanes employed neat or in solution, are effective coupling agents, particularly on fiberglass for further reaction with a broad variety of thermosetting and/or thermoplastic resins.